Agricultura 10: No 1-2: 17-27 (2013)
Copyright 2013 by University of Maribor
Morphological and physiological changes during adventitious root
formation as affected by auxin metabolism: Stimulatory effect of
auxin containing seaweed extract treatment
Andreja Urbanek KRAJNC1*, Maja TURINEK2 and Anton IVANČIČ1
1University of Maribor, Faculty of Agriculture and Life Sciences, Slovenia
2Žipo Lenart, Slovenia
ABSTRACT
The formation of adventitious roots is a quantitative genetic trait regulated by both environmental (especially
temperature, light, relative humidity) and endogenous factors (hormones, sugars, mineral salts and other molecules).
A cutting removed from the stock plant normally undergoes various anatomical changes accompanied by alterations
in metabolic activity and gene expression during the wound response and subsequent rhizogenesis. Rooting consist of
different steps, each with its own hormone requirements. Over recent years, a multitude of models have been proposed
to show how plant hormones and metabolites interact to control adventitious root formation and plant development.
Phytohormones are directly involved in cell division and cell growth, and they indirectly interact with other hormones or
metabolites. Auxin plays an essential role among phytohormones when regulating roots' development and has been shown
to be intimately involved in the process of adventitious rooting. Researchers have developed different rooting treatments,
either by examining the effects of auxin using short exposure to a solution with a high auxin concentration or by dipping in
a rooting powder (auxin with talc). Over the past two decades, auxin-containing seaweed extracts have been recognised as
promising biostimulants for adventitious root formation and plant development. The aim of this review was to summarize
current knowledge associated with the anatomical and physiological aspects of adventitious root formation, and highlight
any recent progress made regarding the identification of auxin-containing seaweed extracts for the control of adventitious
rooting.
Key words: adventitious root formation, auxin, carbohydrates, jasmonate, phenolics, proteins, seaweed extract
Abbreviations: hpe – hours post excision; IAA – indole-3-acetic acid; IBA – indole-3-butyric acid; NAA - 1-naphthalene
acetic acid; PAL - phenylalanine ammonia-lyase; TAL - tyrosine ammonia-lyase; TIBA - triiodobenzoic acid;
ADVENTITIOUS ROOTS AND THEIR FUNCTION
The rooting of stem cuttings is one of the better and
economically-viable propagation methods within agriculture,
horticulture, and forestry. It is governed by an array of
endogenous physiological factors (Druege and Kadner
2008, Osterc and Štampar 2008). Cuttings must survive
physiological stress after severance from the stock plant,
and if receiving little water or nutrient uptake they can be
affected by the usually-reduced stomatal conductance, until
the development of the roots (Druege and Kadner 2008, Pop
et al. 2011). Consequently, chlorophyll loss and an increase in
the xanthophylls cycle-pool are typically associated with leaf
senescence. Further severance-induced metabolic responses
include increased hormone production (auxin, ethylene,
jasmonate) and establishment of a sink tissue, which is
characterised by decreased endogenous carbohydrate status
and the translocation of nutrients to the stem base for
wound healing and cell division (Kadner and Druege 2004;
Rapaka et al. 2005, 2008; Druege and Kadner 2008; Ahkami
et al. 2009; Misra and Misra 2010; Trueman and Richardson
2011). Noticeable progress has been made recently during
research into rooting, which is not a single process but a
progressive process consisting of different steps, each with
its own hormone requirements (de Klerk et al. 1999, Pop et
al. 2011). Physiological characterization, histological analysis
and molecular research on herbaceous and woody plants have
recently provided a proper tool to distinguish these phases.
Ahkami et al. (2009) postulated a three-phase mechanism
for the metabolic response involved during adventitious
root formation (ARF) on petunia used as model herbaceous
plant. (1) The ‘Sink establishment phase’ is characterised by
jasmonate (JA) accumulation immediately after wounding,
and the induction of gene coding for enzymes that degrade
*Correspondence to:
E-mail: [email protected]
17
Morphological and physiological changes during adventitious root
sucrose within the apoplast into hexoses. The hexoses are
taken up by at least one induced monosaccharide transporter
and then used for the production of energy necessary for
wound-healing and cell division. (2) The ‘Recovery phase’
is characterized by the replenishment of resources and
in the petunia it lasts up to 72 hours after excision (hpe)
with the formation of meristemoids. (3) The ‘Maintenance
phase’ is characterized by the symplastic transport of sugars
translocated from the source-leaves into the stem-base. They
are converted, either into intermediates directly flowing into
root development or to the intermediate storage compounds
starch and citrate, thereinafter used for later root formation
processes.
However, there is little information on rooting process
in woody plants. As yet, molecular data are lacking and
physiological studies are scarce. In apple microcuttings,
the timing of three phases was ascertained (De Klerk et al.
1999). During the initial 24 hpe, dedifferentiation of the cells
between the vascular bundles occurs from which the root
primordial originate. These cells accumulate starch during the
initial 24 hours. Wounding-related compounds (breakdown
products of cell membranes, jasmonic acid, cellulase,
pectinase) likely play a major role in the dedifferentitation
phase, probably acting with auxins and cytokinins. Later on,
up to 72 or 96 h, previously activated cells become commited
to the formation of root primordial by the rhizogenic action
of auxin. The starch grains are degraded during the following
24 h (24-48 hpe), the first cell divisions occur 48 hpe, and by
96 hpe, meristemoids are present. The meristemoids develop
into root primordial and afterwards into roots during the
differentitation phase. Indirect rooting of some species, in
which root initials are formed after an intermediate callus
phase, is an obvious example of the occurrence of three phases
with a prolonged period of dedifferentiation. The differences
in auxin requirements among the three phases of adventitious
rooting have important consequences for rooting of cuttings
(De Klerk et al. 1999). Taken together, ARF is modulated
by a combination of different pathways, including hormone
biosynthesis and primary metabolism; the individual steps
exert a control over ARF. In the presented review, a spatiotemporal analysis of hormones and metabolites at different
developmental stages of ARF is provided with respect to
specific anatomical, hormonal and biochemical changes.
MORPHOLOGICAL CHANGES DURING
ADVENTITIOUS ROOT FORMATION
On the basis of anatomical studies, the root formation
phases were designated as the root initiation phase, followed
by the root primordium formation phase, and then the
root elongation and/or emergence phase. These anatomical
events were studied precisely by Ahkami et al. (2009) on
the model plant Petunia hybrida and by De Klerk et al.
(1997, 1999) on apple microcuttings. After the severance of
petunia cuttings from the stock plant, it took 72 h to initiate
the earliest morphological event. This root initiation phase
(Figure 1A) resulted in the occurrence of small cells with
large nuclei and dense cytoplasms – both typical signs of
meristematic cells. On the histological level, starch grains are
18
degraded during the next 24 h, when the first cell divisions
take place and meristemoids appear. The appearance of such
meristemoids marks the transition from the root initiation
phase to the root primordium formation phase (Figure 1B).
This first cytological sign of ARF at 72 hpe was preceded by
the RNA accumulation of the cyclin B1 gene, which might
serve as a marker gene specific for the root initiation phase of
ARF. During the root primordium formation phase, the first
well-developed young root meristems became visible at 96
hpe (Figure 1C). At first globular structures developed root
primordia with the typical dome-shape at 144 hpe, which
included the meristem and behind it the first cells of the root
body. The first roots with elongated cells of the elongation
zone appeared at 192 hpe (Figure 1D). These structures
were still inside the stem, but revealed all the morphology
of a complete root, except for root hairs. They marked the
transition to the root elongation phase, which resulted in the
emerging of the earliest roots, visible after one additional
day.
Figure 1: Anatomy of adventitious root formation
(A-D) in the stem base of pelargonium
(Pelargonium peltatum) cuttings. Typical
stem anatomy consists of epidermis (ep),
cortex (co), pith parenchyma (pi) and a
ring of vessels (r) with outer phloem, the
cambium, and the inner xylem. (A) „Root
initiation phase“: first meristematic cells
(mc) of developing root meristems appear.
(B) „Root primordium formation phase“:
the appearance of an meristemoid (me).
(C) First differentiating root primordia with
an organized meristem and a backward
differentiation of cells of the root body
containing root cortex (ro) and vascular
bundle (v); (D) „Root elongation and/or
emergence phase“: emerging of the first
root with vascular bundles (v) in the center
surrounded by elongated cells (ec) of the
elongation zone. It reaveals morphological
characteristics of the complete root,
except for root hairs.
Morphological and physiological changes during adventitious root
HORMONE CONTROL AND METABOLIC
RESPONSES INVOLVED IN ADVENTITIOUS
ROOT FORMATION
Wound response and the role of jasmonates
The activation of wound-induced responses involves a
complex network of signaling cascades, in which jasmonates
(JA) represent the best-characterized class of signal
molecules. Ahkami et al. 2009 reported that immediate after
wounding, the JA content rose 12-fold and its precursor 12oxo-phytodienoic acid (OPDA) had an approximately 4-fold
accumulation, with a maximum 0.5 hpe. The JA contents
returned to the basal level within 6 hpe, whereas OPDA
remained at the increased level for 6 hours and dropped at
12 hpe to the basal levels. This time-course occurred locally
within the stem base as well as systemically, but at lower
levels, in other parts of the cuttings. Further analyses suggest
that the protein constitutively present within vascular
tissues has constantly high activity and is involved in the
increased biosynthesis of JA, as already shown in the tomato
(Hause et al. 2003, Stenzel et al. 2003). Usually the woundinduced elevation of JA levels is followed by the activation
of JA-responsive genes (Wasternack and House 2002). In
addition, cell wall-invertase transcript accumulation also
seems to be induced by wound-induced JA within the stem
base (Schaarschmidt et al. 2006). Higher levels of transcripts
followed by an increased activity of cell wall invertase might
then lead to a higher sink status of the stem tissue.
AUXIN BIOSYNTHESIS DURING
ADVENTITIOUS ROOT FORMATION
Auxins are a group of tryptophan-derived signals that are
involved in most aspects of plant development (Woodward
and Bartel 2005). Auxin is mainly formed in young leaves
and stem-tips, and is then transported to the roots, both in
the phloem and by a special polar mechanism. Auxins play
a major role in controlling the growth and development of
plants, the early stages of embryogenesis, the organization
of apical meristem (phyllotaxy) and the branching of the
plant’s aerial parts (apical dominance), formation of the
main root, and lateral and adventitious root initiation (Went
and Thimann 1937). Furthermore, it elicits those responses
throughout the plant required for the function of developing
leaves and roots. Auxins are also involved in gravitropism
and phototropism (Kepinski and Leyser 2005). Auxin has a
central role in shoot/root relation, correlating the presence
and development of leaves with root initiation. In addition,
auxin induces the differentiation of vascular tissues, it inhibits
or induces the differentiation of branches and prevents
the abscission of leaves (Sachs 2005, Pop et al. 2011). High
photosynthesis could be coupled with auxin synthesis, thus
enhancing root formation. High ion and water absorptions
could be coupled with high auxin catabolism, thus enhancing
leaf development (Sachs 2005). These multiple effects across
the plant result from its control of cell division, cell elongation,
and certain stages of differentiation. On the cellular level, the
response to auxin includes a rapid initial cell-growth response
that may involve auxin-induced changes in pH, calcium and
gene expression (Davies 2004, Pop et al. 2011).
Rooting-phases have different auxin requirements. There
is always a temporary increase in the endogenous level of
free indol-3-acetic acid (IAA) during the inductive phase
(corresponding to a minimal level of peroxidase/oxidase
activity). The inductive phase is the auxin sensitive, when
the plants are responsive to exogenous auxin application. It
is followed by the auxin insensitive phase (initiation phase)
characterized by a decrease in IAA levels to a minimum and
high peroxidase and oxidase activity (Nag et al. 2001, FaivreRampant et al. 2002). The IAA oxidation at this stage of rooting
(initiation phase) seems to be related to the auxin response.
Oxidation products of IAA may promote root formation,
especially when linked to the phenolic compounds present
(Günes 2000). During the root expressive phase, IAA is again
needed to promote the growth of root’s initials (Štefančič et
al. 2007).
The importance of auxin during the production of lateral
or adventitious roots was demonstrated with several ‘gainof-function’ as well as ‘loss-of-function’ iaa mutations
(Fukaki et al. 2002, Rogg et al. 2001, Tatematsu et al. 2004).
In Arabidopsis, the superroot (sur1 and sur2) mutants,
accumulate IAA, developing numerous adventitious roots
on the hypocotyl and cuttings of different organs in the case
of sur1 (Delarue et al. 1998). Triiodobenzoic acid (TIBA),
an auxin polar transport inhibitor, applied to the top of
the hypocotyls, lowered the rate of root formation (Fabijan
et al. 1981). Rice mutants affected in the expression of the
PIN-FORMED (OsPIN1) gene, potentially involved in auxin
polar transport, are affected in adventitious root emergence
and tillering confirming that the auxin concentrations and
distributions within the different tissues are essential (Xu et
al. 2005).
New insight has been provided over recent years, into the
interaction between auxin and other hormones. Auxin and
ethylene are often described as activators, whilst cytokinins
and gibberellins are seen as inhibitors of adventitious root
formation, even when some positive effects have been
observed. Auxin can increase the rate of ethylene biosynthesis
(Riov and Yang 1989) and stimulate the production of ethylene
correlating with the fact that the ACC synthase4 gene has been
found to be an early auxin-induced gene (Abel et al. 1995).
The auxin and ethylene relations, during root development,
has been shown by a number of isolated mutants that have
resistance to both hormones (Müller et al. 1998, Pan et al.
2002). Studies have emphasized that polyamines play a role
during adventitious rooting (Biondi et al. 1990, Hausman
et al. 1994, Heloir et al. 1996) and a possible interrelation
between polyamines and auxin-controlling rooting induction
has been suggested (Hausman et al. 1995).
In addition over recent years, new insight into the
interaction between auxin and carbohydrates, and their
regulation of ARF, has been provided (Haissig 1989, Roitsch
1999, Druege and Kadner 2008, Agullo-Anton et al. 2011). It
has been reported that auxin stimulates the mobilization of
carbohydrates in leaves and the upper stem, and increases the
translocation of assimilates towards the rooting zone.
19
Morphological and physiological changes during adventitious root
Figure 2: Schematic presentation of the metabolic response during adventitious root formation (ARF) based on
model plants Petunia hybrida and Pelargonium peltatum (modified according to Ahkami et al. 2009,
Urbanek Krajnc et al. 2012). Assimilates are produced in source tissues and translocated towards
the cutting base to establish a sink organ. Wounding induces the accumulation of jasmonates (JA),
which further induce the cell wall invertase (apoInv) transcript accumulation leading to cleavage
of sucrose and transport of hexoses into the cell by monosaccharide transporter STP. Two days
after excision the recovery starts followed by the maintenance phase characterised by symplastic
transport of sugars from source leaves into the stem base and used either for energy production
or accumulated in the vacuole. RuBP – ribulose-1,5-bisphosphate, TP – triose phosphate, E4P –
erythrose-4-phosphate, R5P – ribulose-5-phosphate, FBP – fructose-1,6-bisphosphat, F6P – fructose6-phosphate, S6P – sucrose-6-phosphate, apoInv – apoplastic invertase, cytInv – cytoplasmatic
invertase, vacInv – vacuolar invertase, STP - monosaccharide transporter, TCA cycle – tricarboxylic
acid cycle
THE IMPORTANCE OF CARBOHYDRATES IN ROOTING OF CUTTINGS
Cell division and cell enlargement during ARF require
high input of energy and carbon skeletons. A major carbon
source is sucrose, which is formed in photosynthetically
active tissues and translocated towards the sink-parts of the
plant. Sucrose can be used after cleavage into hexoses as a
direct carbon source or is converted in to storage compounds
20
such as starch (Figure 2). Moreover, there are increasing
indications that sugars have a regulatory role in ARF
(Takahashi et al. 2003, Gibson 2005).
In the stem-bases of petunia cuttings (Ahkami et al. 2009),
the levels of soluble and insoluble sugars start to accumulate
at 24 hpe, despite high metabolic activity from 12 to 24 hpe
onwards. However, the most pronounced increase in sugar
levels was documented during the later stages of ARF. A
continuous increase of sucrose within source leaves can
be observed from 144 hpe onwards, probably owing to an
Morphological and physiological changes during adventitious root
increased photosynthetic capacity. This sucrose can be
translocated towards the stem base for further metabolism.
The basipetal translocated sucrose is, however, not only used
for delivering energy for differentiation (cell division and
cell enlargement), but considerable portion of the sucrose
is converted into starch, which probably acts as the major
carbon source when the adventitious roots are growing.
As shown for Pinus radiata, sucrose applied to a growingmedium leads to higher levels of sugars and starch in the
rooting regions of the hypocotyl cuttings, and enhances root
formation (Li and Leung 2000). The analyses of Ahkami
et al. (2009) indicated that starch can be synthesized and
stored in different cell types in order to meet their demand
for increased metabolic activity when the adventitious roots
emerge (Ahkami et al. 2009).
In agreement with the low sucrose content, directly after
excision (»sink establishment phase«), at the cutting base
the cell wall invertase activity was increased during the first
hours after excising, and decreased again to the basal level
before root formation. By contrast, the activities of vacuolar
and cytosolic invertases decreased continuously to a low level
(Ahkami et al. 2009). Cell wall invertase is not only a key
enzyme of the apoplastic phloem unloading of transported
sucrose but also links phytohormone action with primary
metabolism (Roitsch and González 2004). Being present
within the apoplast, it can establish the sink function of
a certain tissue and thus provide a mechanism for flexible
and appropriate adjustment to a wide range of internal and
external stimuli (Roitsch et al. 2003). The metabolic activity
through which the hexoses from the basipetal transported
sucrose can be catabolized leads to successive increases in
both, phosphofructokinase (PFK) and glucose-6-phosphate
dehydrogenase (Glc6P DH) activities, and a decrease in
the cytosolic fructose-1,6-bisphosphatase activity. These
events strongly suggest that the catabolism of glucose occurs
in parallel within the pentose phosphate pathway and by
glycolysis. This yields ATP as energy-source and amino acids
for protein synthesis (Ahkami et al. 2009).
The importance of carbohydrates in ARF of pelargonium
cuttings and the effects of carbohydrate shortage were
studied by Druege and Kadner (2008). Especially, rooting
of dark-stored pelargonium cuttings can be restricted by
carbohydrate shortage resulting from the interplay between
depleted carbohydrate reserves and weak photosynthesis
under the low light conditions in the winter’s in Central
Europe. Druege and Kadner 2008 assumed that considerably
reduced air temperature during rooting increased the current
availability of carbohydrates, thereby improving survival and
root formation. Higher sugar levels during rooting, mediated
by low air temperature (10 °C, root zone temperature: 20
°C) were positively correlated with reduced leaf senescence,
a higher survival rate, and a higher number of roots. The
authors thus provided new prospects for the control of air
temperature during the rooting of cuttings that exhibit low
current photosynthesis.
AMINO ACIDS AND PROTEIN METABOLISM DURING ADVENTITIOUS ROOT
FORMATION
In most of the plant systems analyzed, the most abundant
amino acids in vascular tissues were glutamate, glutamine
and, in some cases, asparagine (Urquhart and Joy 1982,
Schobert and Komor 1989, Lohaus and Moellers 2000).
Analysis of the petunia stems before excision indicated that
mainly glutamine and asparagine were synthesized in the
source-tissues and transported downwards to the sink-tissues
(Ahkami et al. 2009). Since glutamine biosynthesis is the key
step of nitrate assimilation in plants (Joy 1988) and supplies
nitrogen for amino acid synthesis, the basipetal translocation
of glutamine is an important process to meet the demands
of the cells during root-formation. Levels of glutamine and
asparagine remained low at the later stages. This indicated
a high turnover of the translocated amino acids into others
that appear to be essential for accelerated protein synthesis
during ARF (Druege and Kadner 2008, Ahkami et al. 2009).
A similar response was also determined for proteins in the
case of pelargonium cuttings. In the presented experiment,
a transient decline in total protein values was monitored
twenty-three days after the severance of pelargonium cuttings
(Urbanek Krajnc et al. 2012). However, this decline can not
only be linked to the establishment of a sink-tissue and
adequate mobilisation of primary metabolites to the region
of root regeneration. Recent analyses of tomatos suggested
that the proteins and amino acids constitutively presented in
vascular tissues are involved in the increased biosynthesis of
jasmonates, the best-characterised class of signal molecules
involved in wound-induced responses (Hause et al. 2003).
Jasmonate accumulation induces genes coding for invertases
that degrade sucrose within the apoplast to hexoses used
for the production of energy necessary for wound healing
and cell devision. In the petunia stems' cuttings, the strong
depletion of total amino acids between 6 and 48 hours after
excision was measured and, thereafter, a recovery reaching
only 50 % of the initial value was observed (Ahkami et al.
2009). These same authors confirmed a change of carbon
to nitrogen ratio in petunias towards a threefold increase of
carbon against nitrogen, beginning 48 hours post excision.
The analysis of petunia stems pre-excision confirmed that
mainly glutamine and asparagine were synthetised in source
tissues and transported downwards to the sink tissues. Since
glutamine biosynthesis is the key step of nitrate assimilation
in plants and supplies nitrogen for amino acid synthesis (Taiz
and Zeiger 2010), a basipetal translocation of glutamine is
an important process for meeting the demands of the cells
during root formation. These early events in ARF described
by different authors would explain the observed depletion of
protein contents within pelargonium cuttings 23 days post
severance. Later on (36 dps), a strong increase was determined
in the protein levels of pelargonium leaves (Urbanek Krajnc
et al. 2012), which would be parallel to an increase in the
carbohydrates due to high photosynthesis rates.
21
Morphological and physiological changes during adventitious root
ROLE OF PHENOLICS DURING
ADVENTITIOUS ROOT FORMATION
Severance from the stock plant, induces the biosynthesis
of phenolic compounds, which is why many authors have
detected an increased phenolic content level during the
first days after establishing the cuttings (Osterc et al. 2004,
Quaddoury and Amssa 2004, Štefančič et al. 2007, Osterc
and Štampar 2008). Several results have indicated that
some phenolic compounds (chlorogenic acid, epicatechin,
caffeic acid, catechol, gallic acid, ferulic acid) act as rooting
co-factors during the root formation process, especially as
protectors of IAA against oxidation. On the other hand, the
presense of specific phenolic compounds (sinapinic acid,
vanillic acid, cinnamic acid) have a negative impact on ARF
during the vegetative propagation of cuttings (Osterc et al.
2004, Trobec et al. 2005). Focusing on IAA protectors, two
modes of action are ascribed: they might act as competing
oxidation substrates for IAA-oxydase instead of IAA, or more
likely they may function as free radical scavengers that drive
the peroxidase-catalysed reaction (Trobec et al. 2005; Osterc
et al. 2007, 2008; Štefančič et al. 2007; Osterc and Štampar
2008). Higher amounts of these phenolic substances mean
more IAA in this way. Thus fluctuation of phenol contents
during adventitious rhizogenesis undergoes a time-course
variation paralleling that of free IAA, which is generally
credited as the trigger for root initiation, and the physiological
stages of rooting are correlated with changes in endogenous
auxin concentrations (Bartel et al. 2001, Faivre-Rampant et
al. 2002, Pop et al. 2011).
In the presented study, an increased accumulation of total
phenolics three weeks after the establishment of pelargonium
cuttings coincided with a decrease in total protein levels
(Urbanek Krajnc et al. 2012). These results are in agreement
with current knowledge that the synthesis of phenolics is
coupled with amino acid metabolism and controlled by
enzymes, including phenylalanine ammonia-lyase (PAL)
and tyrosine ammonia-lyase (TAL). These enzymes act
through the deamination of phenylalanine and tyrosine to
yield t-cynnamic and p-coumaric acids, respectively, with the
liberation of ammonia (Taiz and Zeiger 2010).
Thirty six days after severance, a slight decline in
total phenolics was measured in pelargonium cuttings in
comparison to the previous sampling (Urbanek Krajnc
et al. 2012). A similar time-course of changes in phenolic
contents has also been described by other authors (Trobec
et al. 2005, Štefančič et al. 2007, Osterc and Štampar 2008).
These authors first recorded increases in certain phenolic
compounds in the leaves of chestnut cuttings, and the basal
portions of cherry cuttings during rooting, later on the
concentrations of monophenols rapidly decreased, especially
sinapinic acid and vanillic acid, to which a negative influence
on rooting is ascribed. Štefančič et al. (2007) reported that
the fluctuation of phenolic content undergoes a time-course
variation that parallels that of free IAA. A time-course
analysis of single phenolic compounds and enzymes involved
in the phenylpropanoid pathway would provide a better
understanding of the interactions amongst indole-3-butyric
acid (IBA) and phenolics during adventitous root formation
in the future.
22
THE SIGNIFICANCE OF ENDOGENOUS
AND EXOGENOUS AUXIN IN CONTROL
OVER ADVENTITIOUS ROOT FORMATION
Auxin is one of the major endogenous hormones involved
in the process of adventitious rooting and the physiological
stages of rooting are correlated with changes in endogenous
auxin concentrations. Plants produce IAA in the shoot apices
and in young leaves. After detachment of the shoot, basipetal
polar transport of auxin contributes to auxin accumulation
in the stem base and the rise of free auxin in the basal stem
very probably contributes to the early events of adventitious
root formation (Ahkami et al. 2009). However, for successful
rooting in difficult-to-root plant species, exogenous
application of auxin can contribute significantly to the plant’s
auxin-pool and promote adventitious root formation (Pop
et al. 2011). IAA was the first used to stimulate rooting of
cuttings (Cooper 1935) and soon afterwards other auxins
that also promoted rooting, IBA and NAA (1-naphthalene
acetic acid) were synthesized chemically and were considered
even more effective (Zimmerman and Wilcoxon 1935). Talc
powder was introduced as a carrier for auxin (Grace 1937).
Nowadays IBA is used for rooting during commercial
operations, followed by IAA and NAA, and the chemical
analogues synthesized and examined for auxin-like activities.
Auxin mostly enters cuttings via the cut surface (Kenney et
al. 1969), even in microcuttings that are known to have a
poorly functioning epidermis (Guan and De Klerk 2000),
and is rapidly taken up in cells by pH trapping (Rubery and
Sheldrake 1973) and by influx carriers (Delbarre et al. 1996).
Auxin metabolism studies on adventitious rooting have been
done on cuttings exposed to auxin over a prolonged period,
but in other studies cuttings have been exposed to auxin over
short periods (Diaz-Sala et al. 1996, Liu and Reid 1992) It
was recognised, that an optimal auxin concentration for one
of the three phases may be supraoptimal or suboptimal for
the next. Over recent years, a multitude of models have been
proposed for showing how auxin interacts for controlling
adventitious root formation (ARF) and plant development
(Sachs 2005, Jaillas and Chory 2010, Agullo-Anton et al. 2011,
Pop et al. 2011). Although roots may be induced by auxin,
it must be taken into a account that wounding is usually
required to achieve rooting and it was suggested that WRCs
(wounding-related compounds) play a major role during the
de-differentiation phase (de Klerk et al. 1999).
When applying exogenous IBA on cuttings, the endogenous
auxin concentration reaches a peak after wounding,
thus coinciding with the initation of the rooting process.
Interaction between endogenous IAA and exogenous IBA
during ARF has been suggested and the performance of IBA
versus IAA explained regarding several possibilities: higher
stability, differences in metabolism, differences in transport,
and IBA as a slow release source of IAA. Biochemical studies
in numerous plants, and genetic studies of Arabidopsis IBAmutants, indicate that IBA acts primarily via its conversion
to IAA, which occurs through a mechanism similar to
peroxisomal fatty acid b-oxidation; however, some evidence
suggests that IBA acts as an auxin on its own (Pop et al.
2011).
Morphological and physiological changes during adventitious root
The applied auxins are reported to lower the IAA
oxidation, and this might reduce the consumption of phenolic
antioxidants, which play a very important role as protectors
of the IAA against oxidation (Volpert et al. 1995, Krylov et al.
1995, De Klerk et al. 1999)
Štefančič et al. (2007) investigated the influence of
exogenous indole-3-acetic acid (IAA) and indole-3-butyric
acid (IBA) on changes in the internal levels of IAA, indole3-acetylaspartic acid (IAAsp) and antioxidant phenolics
(chlorogenic acid and epicatechin) during the first 5 days of
adventitious root formation in leafy cuttings of the cherry
rootstock ‘GiSelA 5’. The highest free and conjugated IAA
accumulations in the cutting bases were observed in the IAA
treated cuttings, but that did not promote the percentage of
cuttings rooted. IBA gave the best propagation results, as 80%
of cuttings formed roots during the first month of rooting.
This indicates the influence of IBA on early root development,
independently of IAA (Štefančič et al. 2007). Similarly, it was
also reported for Malus microcuttings. IBA induced more
roots than IAA although it was converted to IAA only at very
low levels, suggesting that either IBA itself was active or that
it modulated the activity of IAA (Van Der Kriken et al. 1992).
Many other investigations have shown that IBA (indole-3butyric acid) has a greater ability to promote adventitious root
formation in comparison to IAA (Spethmann and Hamzah,
1988; Riov, 1993; De Klerk et al., 1999; Ludwig-Müller, 2000).
It is more stable and less sensitive to the auxin degrading
enzymes (Nordström et al. 1991; Epstein and LudwigMüller, 1993; Riov 1993). IAA is rapidly metabolized by the
peroxidase, acting as an IAA-oxidase, with the strongest
activity during the root initiation phase (Caboni et al. 1997,
Nag et al. 2001). IAA is partially protected against oxidation
when transformed into one of its conjugated forms, from
amongst which IAAsp (indole-3-acetylaspartic acid) is the
more abundant in various plant species (Norcini and Heuser
1988, Nordström et al. 1991). Rapid conjugation also prevents
the overaccumulation of IAA within the tissue, which is a
more common occurrence in exogenous auxin applications
(Faivre-Rampant et al. 2002). When hydrolyzed, IAAsp can
serve as a slowly released source of free auxin during the
advanced stages of the rooting process (Epstein and LudwigMüller 1993; Riov 1993). IBA conjugates are an even better
source of free auxin, because they are more resistant to the in
vivo degradation, whilst IAAsp is subjected to oxidation into
biologically inactive products (Riov 1993).
Several other positive physiological effects of IBA
treatment have been recognised over recent years. It has
been demonstrated that exogenous IBA, when applied to the
rooting zone, activates the sugar metabolism that releases
energy and provides carbon skeletons for the synthesis of
other essential compounds such as proteins (Agullo-Anton et
al. 2011). Furthermore, IBA is reported to increase the rate of
ethylene biosynthesis, and an auxin-ethylene relation during
root development has been shown by the number of isolated
mutants that have resistance to both hormones (Sachs 2005,
Werner et al. 2008, Perilli et al. 2010, Pop et al. 2011).
Several authors reported that the stimulation of ARF in
cuttings by exogenous indole-3-acetic acid coincided with
increased sugar availability at the site of root primordial
development. It was discovered that exogenous auxin
applied to the rooting zone stimulates the mobilization of
carbohydrates in leaves and the upper stem and increases
the translocation of assimilates towards the rooting zone
in order to release energy, and provides carbon skeletons
for the syntheses of other essential compounds such as
proteins (Haissig 1989). Auxin application to the stem base
of carnation cuttings raised sugar levels within the same
tissues during rooting and counteracted the transient sugar
depletion in leaves (Agullo-Anton et al. 2011).
SEAWEEDS ARE AN IMPORTANT
SOURCE OF HORMONES
Seaweeds are an important source of plant growth
regulators, together with organic osmolites, amino acids,
mineral nutrients, vitamins, and vitamin precursors.
Over recent years, the use of natural seaweed as a plant
growth stimulant has allowed for its substitution in place
of conventional synthetic growth regulators and fertilizers
(Sahoo 2000, Khan et al. 2009). In particular, Kelpak®
[Kelpak® Kelp Products (Pty) Ltd] contains 11 mg/L IBA,
and 0.031 mg /L kinetin, as well as a high amount of amino
acids, vitamins, and mineral nutrients. This biostimulant is
prepared by a cell burst process from brown algae Ecklonia
maxima (Osbecki) Papenfuss, located in the cold waters along
the Atlantic coast of Southern Africa. Recent reports have
shown that low levels of Ecklonia maxima concentrate, when
applied as a foliar spray or root drench, increases seedlings’
qualities and survival, improves root-growth, vegetative and
reproductive growth, flowering, fruit production, and the
yields of many crop plants and vegetables (Crouch and van
Staden 1993, 1994; van Staden et al. 1994; Kowalski et al.
1999; Arthur et al. 2003; Khan et al. 2009). Whilst there is a
growing acceptance that seaweed liquid fertilizers (SLF) are
tools when addressing the need for improved current crop
production practices for long-term sustainability, the margin
for beneficial action regarding Kelpak® during the vegetative
propagation of ornamental cuttings, was found to be rather
narrow. Urbanek Krajnc et al. (2012) performed a time-course
analysis of the photosynthetic pigment, phenolic, and protein
contents within the leaf tissues of Pelargonium peltatum 'Ville
de Paris Red' from the initial cuttings to market maturity, in
regard to brown algae [Ecklonia maxima (Osbeck) Papenfuss]
extract treatment (Kelpak®). A positive impact by the 0.5%
and 1% Kelpak® treatment on the protein accumulation
within the leaves of pelargoniums was monitored. Elevated
protein contents within the Kelpak®treated samples could be
attributed to a high concentration of IBA within the Kelpak®
extract, since it is well-known that IBA has a positive-effect on
those enzymes involved in nitrogen assimilation (Kaur et al.
2002, Hayat et al. 2009). Beside the exogenous IBA, kinetin,
and other seaweed components, especially nitrogen, amino
acids, and vitamins, may have a synergistic impact on protein
accumulation within Kelpak®treated cuttings. The results are
in accordance with other seaweed treatment experiments.
For example, Beckett et al. (1994) indicated increased levels
of nitrogen within the leaves of nutrient-stressed tepary
beans after treatment with Kelpak®. Furthermore, increased
23
Morphological and physiological changes during adventitious root
total protein values were also reported in Arachys hypogaea
by Sridhar and Rengasamy (2010) after treatment with brown
algae Sargassum wightii extract.
Kelpak® treatment was also found to significantly affect
the concentration of phenolic compounds within the
pelargonium leaves (Urbanek Krajnc et al. 2012), thus the
involvement of IBA in phenylpropanoid pathways was
hypothesized. Similarly, Fan et al. (2011) reported that root
treatment with brown algae (Ascophyllum nodosum) extract
elicits the phenylpropanoid and flavonoid pathways in
spinach, but the mechanism remains unexplained.
In our previous study (Urbanek Krajnc et al. 2012), we also
demonstrated that Kelpak® treatment of Pelargonium peltatum
Ville de Paris Red' cuttings can maintain the functionally
active green leaves due to increased photosynthetic pigment
accumulation, thus improving the ‘whole plant’ functional
integrity following the insertions of cuttings into the soil.
Maintaining the functionally active green leaves during
root induction is crucial, since root formation relies on an
adequate supply of carbohydrates from the source leaves to
the region of root regeneration (Druege and Kadner 2008).
Carbohydrate depletion is compensated for by current
photosynthesis (Haissig 1989, Rapaka et al. 2005, Ahkami
et al. 2009, Agullo-Anton et al. 2011). However, the excised
cuttings of most plant species, including control pelargonium,
show low photosynthetic rates, a decrease in chlorophyll
contents and an increase in β-carotene and lutein unless first
roots are formed, which could be explained by lower water
potential due to severance of cuttings (Druege and Kadner
2008, Urbanek Krajnc et al. 2012). In contrast, Kelpak® treated
pelargonium cuttings showed higher pigment concentrations
when compared to the controls, reflecting a readjustment of
the photosynthetic carbon metabolism. Urbanek Krajnc et al.
(2012) assumed that the presence of IBA in the Kelpak®extract
may increase chlorophyll concentration in leaves of cuttings.
It was reported previously that IBA treatments cause an
enhancement of chlorophyll contents within different stem
cuttings (Mustafa 1996, Kaur et al. 2002). Furthermore,
seaweed products are known to enhance plant chlorophyll
content and reduce leaf senescence as a result of a reduction
in chlorophyll degradation, which might be caused in part
by betaines within the seaweed extract (Khan et al. 2009). It
has been reported recently that SLF prepared from different
brown algae species has a beneficial effect on photosynthetic
pigments' contents. The application of SLF derived from
the brown algae Ascophyllum nodosum in combination
with standard fertilization, increased the leaf chlorophyll
content, photosynthesis, and transpiration rates in tomato,
cucumber, dwarf French beans, wheat, barley,maize, apples,
grapes, and strawberries (Blunden 1991, Whapham et al.
1993, Blunden et al. 1997, Spinelli et al. 2010). Thirumaran
et al. (2009) reported that, a SLF prepared from the brown
algae Rosenvingea intricata, increased the total chlorophyll
and carotenoids in Cyamopsis tetragonoloba. Furthermore,
Sridhar and Rengasamy (2010) reported that groundnut
treated with Sargassum wightii extract showed enhanced
concentrations of photosynthetic pigments in leaves.
Nethertheless, the biostimulatory effect of Kelpak®
treatment on primary and secondary metabolism of
pelargonium cuttings was reflected in significantly
24
increased root fresh mass, shoot/root ratio, and maximum
number of leaves (Urbanek Krajnc et al. 2012). To sum up,
higher photosynthetic pigment concentrations in cuttings
treated with auxin-containg SLF, significantly contribute to
increased photosynthetic activity and enhanced production
of photoassimilates. Consequently, higher sugar levels during
rooting are positively correlated with less expressed leaf
senescence, higher survival rate, increased root formation
and more efficient nutrients' uptake of cuttings.
CONCLUSIONS
In the presented review, causal interactions between
auxins and specific primary and secondary metabolites
were analysed during the process of ARF. It has been
shown how the applications of different auxin sources or
compounds inhibiting basal auxin transport modulate
different metabolites during ARF. Taken together, exogenous
auxin application promotes ARF in several ways. It has
a direct influence on root induction at the stem bases of
cuttings, as well as a stimulatory effect on sink activity and
the translocation of assimilates towards the stem base. Auxin
further inhibits leaf senescence, increases the chlorophyll
contents and the photosynthesis in leaves, and accounts for
the plasticity of shoot/root relations.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
Abel S, Nguyen MD, Chow W, Theologis A. ACS4, a
primary indoleacetic acid-responsive gene encoding
1-aminocyclopropane-1-carboxylate
synthase
in
Arabidopsis thaliana. Structural characterization,
expression in Escherichia coli, and expression
characteristics in response to auxin [corrected]. J. Biol.
Chem. 1995;270(32):19093-19099.
Agullo-Anton MA, Sanchez-bravo J, Acosta M, Druege
U. Auxins or Sugars: What Makes the Difference in the
Adventitious Rooting of Stored Carnation Cuttings? J.
Plant Grow. Regul. 2011;30:100-113.
Ahkami AM, Lischewski S, Haensch, KT, Porfirova S,
Hofmann J, Rolletschek H, Melzer M, Franken P, Hause
B, Druege U, Hajirezaei MR. Molecular physiology
of adventitious root formation in Petunia hybrid
cuttings: involvement of wound response and primary
metabolism. New Phytol. 2009;181:613-625.
Arthur GD, Stirk WA, van Staden J. Effect of a seaweed
concentrate on the growth and yield of three varieties of
Capsicum annuum. S. Afr. J. Bot. 2003;69:207–211.
Bartel B, LeClere S, Magidin M, Zolman BK. Inputs to
the active indole-3-acetic acid pool: de novo synthesis,
conjugate hydrolysis, and indole-3-butyric acid
β-oxidation. J. Plant Grow. Regul. 2001;20:198–216.
Beckett RP, Mathegka ADM, Staden J. Effect of seaweed
concentrate on yield of nutrient-stressed tepary bean
(Phaseolus acutifolius Gray). J. Appl. Phycol. 1994;6:429430.
Biondi S, Diaz T, Iglesias I, Gamberini G, Bagni N.
Polyamines and ethylene in relation to adventitious
Morphological and physiological changes during adventitious root
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
root formation in Prunus avium shoot cultures. Physiol.
Plant. 1990;78(3):474-483.
Blunden, G. Agricultural uses of seaweeds and seaweed
extracts. In: Guiry M.D., Blunden G., 1991, “Seaweed
Resources in Europe; Uses and Potential”. Chichester,
UK: John Wiley & Sons, 1991,65-81.
Blunden G, Jenkins T, Liu YW. Enhanced leaf chlorophyll
levels in plants treated with seaweed extract. J. Appl.
Phycol. 1997;8:535-543.
Caboni E, Tonelli MG, Lauri P, Iacovacci P, Kevers C,
Damiano C, Gaspar T. Biochemical aspects of almond
microcuttings related to in vitro rooting ability. Biol.
Plant. 1997;39:91–97.
Cooper WC. Hormones in relation to root formation on
stem cuttings. Plant Physiol. 1935; 10:789-794
Crouch IJ, van Staden J. Commercial seaweed products
as biostimulants in horticulture. J. Home Consum.
Hortic. 1994;1:19-76.
Davies PJ. Plant hormones: Biosynthesis, signal
transduction, action! Dordrecht, Kluwer Academic
Publishers, The Netherlands. 2004.
De Klerk GJ, Armholdt-Schmitt B, Lieberei R, Neumann
KH. Regeneration of roots, shoots and embryos:
physiological, biochemical and molecular aspects. Biol.
Plant. 1997;39:53-66.
De Klerk GJ, van der Krieken W, de Jong J. Review
the formation of adventitious roots: New concepts,
new possibilities. In Vitro Cell Dev. Biol. Plant.
1999;35(3):189-199.
Delarue M, Prinsen E, Onckelen HV, Caboche M, Bellini
C. Sur2 mutations of Arabidopsis thaliana define a new
locus involved in the control of auxin homeostasis. Plant
J. 1998;14(5):603-611.
Delbarre A, Müller P, Imhoff V, Guern J. Comparison
of mechanisms controlling uptake and accumulation of
2,4-dichlorophenoxy acetic acid, naphthalene-1-acetic
acid, and indole-3-acetic acid in suspension-cultured
tobacco cells. Planta 1996;198:532-541.
Diaz-Sala C, Hutchison KW, Goldfarb B, Greenwood
MS. Maturation-related loss in rooting competence by
loblolly pine stem cuttings: The role of auxin transport,
metabolism and tissue sensitivity. Physiol. Plant
1996;97(3):481-490.
Druege U, Kadner R. Response of post-storage
carbohydrate levels in pelargonium cuttings to reduced
air temperature during rooting and the relationship
with leaf senescence and adventitious root formation.
Postharvest Biol. Tec. 2008;47:126-135.
Epstein E, Ludwig-Muller J. Indole-3-butyric acid in
plants: occurrence, synthesis, metabolism and transport.
Physiol. Plant 1993;88:382–389.
Fabijan D, Taylor JS, Reid DM. Adventitious rooting in
hypocotyls of sunflower (Helianthus annuus) seedlings.
Physiol. Plant 1981;53(4):589-597.
Faivre-Rampant O, Charpentier JP, Kevers C, Dommes
J, van Onckelen H, Jay-Allemand C, Gaspar T. Cuttings
of the non-rooting rac tobacco mutant overaccumulate
phenolic compounds. Funct. Plant Biol. 2002;29:63-71.
Fan D, Hodges M, Zhang J, Kirby CW, Ji X, Locke SJ,
Critchley AT, Prithiviraj B. Commercial extract of
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
the brown seaweed Ascophyllum nodosum enhances
phenolic antioxidant content of spinach (Spinacia
oleracea L.) which protects Caenorhabditis elegans
against oxidative and thermal stress. Food Chem.
2011;124:195-202.
Fukaki H, Tameda S, Masuda H, Tasaka M. Lateral root
formation is blocked by a gain-of-function mutation
in the SOLITARY-ROOT/IAA14 gene of Arabidopsis.
Plant J. 2002;29(2):153-168.
Gibson SI. Control of plant development and gene
expression by sugar signaling. Curr. Opin. Plant Biol.
2005;8: 93–102.
Grace NH. Physiologic curve of response to
phytohormones by seeds, growing plants, cuttings and
lower plant forms. Can. J. Res. C. 1937;15:538-546.
Guan H, De Klerk GJ. Stem segments of apple
microcuttings take up auxin predominantly via the cut
surface and not via the epidermal surface. Sci. Horti.
2000;86:23-32
Günes T. Peroxidase and IAA-oxidase activities during
rooting in cuttings of three poplar species. Turk. J. Bot.
2000;24:97–101.
Haissig BE. Carbohydrate relations during propagation
of cuttings from sexually mature Pinus banksiana trees.
Tree Phys. 1989;5:319-328.
Hause B, Hause, G, Kutter C, Miersch O, Wasternack
C. Enzymes of jasmonate biosynthesis occur in tomato
sieve elements. Plant Cell Physiol. 2003;44:643-648.
Hausman JF, Gevers C, Gaspar T. Involvement of
putrescine in the inductive rooting phase of poplar
shoots raised in vitro. Physiol. Plant 1994;92(2):201206.
Hausman JF, Gevers C, Gaspar T. Auxin-polyamine
interaction in the control of the rooting inductive phase
of poplar shoots in vitro. Plant Sci. 1995;110(1):63-71.
Hayat Q, Hayat S, Barket A, Aqil A. Auxin analogues
and nitrogen metabolism, phtosynthesis, and yield of
Chickpea. J. Plant Nut.2009;32:1469-1485.
Heloir MC, Kevers C, Hausman JF, Gaspar T. Changes
in the concentrations of auxins and polyamines during
rooting of in-vitro-propagated walnut shoots. Tree
Physiol. 1996;16(5):515-519.
Jaillas Y, Chory J. Unraveling the paradoxies of plant
hormone signaling integration. Nat. Struct. Mol. Biol.
2010;17:642-645.
Joy KW. Ammonia, glutamine and asparagine: a carbonnitrogen interface. Can. J. Bot. 1988;66:2103–2109.
Kadner R, Druege U. Role of ethylene action in
ethylene production and poststorage leaf senescence
and survival of pelargonium cuttings. J. Plant Grow.
Regul. 2004;43:187–196.
Kaur S, Cheema SS, Chhabra BR, Talwar KK. Chemical
induction of physiological changes during adventitious
root formation and bud break in grapevine cuttings. J.
Plant Grow. Regul. 2002;37:63-68.
Kenney G, Sudi J, Blackman GE. The uptake of growth
substances XIII. Differential uptake of indole-3yl-acetic
acid through the epidermal and cut surfaces of etiolated
stem segments. J. Exp. Bot. 1969;20:820-840.
Kepinski S, Leyser O. Plant development: auxin in loops.
25
Morphological and physiological changes during adventitious root
Curr. Biol. 2005;15(6):208-210.
41. Khan W, Rayirath UP, Subramanian S, Jithesh MN,
Rayorath P, Hodges DM, Critchley AT, Craigie JS,
Norrie J, Prithiviraj B. Seaweed extracts as biostimulants
of plant growth and development. J. Plant Grow. Regul.
2009;28:386–399.
42. Kowalski B, Jäger AK, van Staden J. The effect of a seaweed
concentrate on the in vitro growth and acclimatization
of potato plantlets. Potato Res. 1999;42:131–139.
43. Krylov SN, Aguda BD, Ljubimova ML. Bistability and
reaction thresholds in the phenol-inhibited peroxidasecatalyzed oxidation of indole-3-acetic acid. Biophys.
Chem. 1995;53:213–218.
44. Li M, Leung DWM. Starch accumulation is associated
with adventitious root formation in hypocotyl cuttings
of Pinus radiata. J. Plant Grow. Regul. 2000;19:423
–428.
45. Liu HJ, Reid DM. Auxin and ethylene-stimulated
adventitious rooting in relation to tissue sensitivity to
auxin and ethylene production in sunflower hypocotyls.
J. Exp. Bot. 1992;43:1191-1198.
46. Lohaus G, Moellers C. Phloem transport of amino acids
in two Brassica napus L. genotypes and one B. carinata
genotype in relation to their seed protein content. Planta
2000;211:833–840.
47. Ludwig-Müller J. Indole-3-butyric acid in plant growth
and develop-ment. Plant Growth Reg. 2000;32:219–
230.
48. Misra M, Misra AN. Changes in photosynthetic
quantum yield of developing chloroplasts in lotus
(Nelumbo nucifera Gaertn.) leaf during vegetative, bud
and flowering stages. Afr. J. Plant Sci. 2010;4:179-182.
49. Müller A, Guan C, Galweiler L, Tanzler P, Huijser P,
Marchant A, Parry G, Bennett M, Wisman E, Palme
K. 9AtPIN2 defines a locus of Arabidopsis for root
gravitropism control. Embo. J. 1998;17(23):6903-6911.
50. Mustafa MM. Effect of indole-3-butyric acid and some
nutrient elements on rooting of hydrangea cuttings.
Alexandria J. Agricult. Res. 1996;41:237-246.
51. Nag S, Saha K, Choudhuri MA. Role of auxin and
polyamines in adventitious root formation in relation
to changes in compounds involved in rooting. J. Plant
Growth Regul. 2001;20:182–194.
52. Norcini JG, Heuser CW. Changes in the level of [14C]
Indole-3-acetic acid and [14C]Indoleacetylaspartic acid
during root formation in mung bean cuttings. Plant
Physiol. 1988;86:1236–1239.
53. Nordstrőm AC, Jacobs FA, Eliasson, L.Effect of
exogenous indole-3-acetic acid and indole-3-butyric
acid on internal levels of the respective auxins and their
conjugation with aspartic acid during adventitious root
formation in pea cuttings. Plant Physiol. 1991;96:856–
861.
54. Osterc G, Trobec M, Usenik V, Solar A, Štampar F.
Changes in polyphenols in leafy cuttings during the
root initiation phase regarding various cutting types at
Castanea. Phyton (Horn, Austria). 2004;44:109–119.
55. Osterc G, Štefančič M, Solar A, Štampar F. Potential
involvement of flavonoids in the rooting response of
chestnut hybrid (Castanea crenata × Castanea sativa)
26
clones. Aust. J. Exp. Agr. 2007;47:96-102.
56. Osterc G, Štampar F. Initial cutting lenght modifies
polyphenol profile in Castanea cuttings during the root
formation process. Eur. J. Hortic. Sci. 2008;73:201-204.
57. Osterc G, Štefančič M, Solar A, Štampar F. Phenolic
acids affect rooting in chestnut hybrid clones (Castanea
crenata × Castanea sativa). Acta Agr. Scand., Section B:
Soil & Plant Science 2008;58:162-168.
58. Pan R, Wang J, Tian X. Influence of ethylene on
adventitious root formation in mung bean hypocotyl
cuttings. Plant Grow. Regul. 2002;36(2):135-139.
59. Perilli S, Moubayidin L, Sabatini S. The molecular basis
of cytokinin function. Curr. Opin. Plant Biol. 2010;13:
21-26.
60. Pop TI, Pamfil D, Bellini C. Auxin Control in the
Formation of Adventitious Roots. Not. Bot. Hort.
Agrobot. Cluj. 2011;39:307-316.
61. Quaddoury A, Amssa M. Effect of exogenous indole
butyric acid on root formation and peroxidase and
indole-3-acetic acid oxidase activities and phenolic
contents in date palm offshoots. Bot. Bull. Acad. Sinica.
2004;45:127–131.
62. Rapaka VK, Bessler B, Schreiner M, Druege U. Interplay
between initial carbohydrate availability, current
photosynthesis, and adventitious root formation in
Pelargonium cuttings. Plant Sci. 2005;168:1547–1560.
63. Rapaka VK, Faust JE, Dole JM, Runkle ES. Endogenous
carbohydrate status affects postharvest ethylene
sensitivity in relation to leaf senescence and adventitious
root formation in Pelargonium cuttings. Postharvest
Biol. Tec. 2008;48:272–282.
64. Riov J, Yang S. Ethylene and auxin-ethylene interaction
in adventitious root formation in mung bean (Vigna
radiata) cuttings. J. Plant Grow Reg. 1989;8(2):131-141.
65. Riov J. Endogenous and exogenous auxin conjugates in
rooting of cuttings. Acta Hortic. 1993; 329: 284–288.
66. Rogg LE, Lasswell J, Bartel B. A gain-of-function
mutation in IAA28 suppresses lateral root development.
Plant Cell 2001;13(3):465-480.
67. Roitsch T. Source-sink regulation by sugar and stress.
Curr. Opin. Plant Biol. 1999;2:198-206.
68. Roitsch T, Balibrea ME, Hofmann M, Proels R, Sinha
AK. Extracellular invertase: key metabolic enzyme and
PR protein. J. Exp. Bot. 2003;54:513–524.
69. Roitsch T, González MC. Function and regulation
of plant invertases: sweet sensations. T. Plant Sci.
2004;9:606–613.
70. Rubery PH, Sheldrake AR. Effect of pH and surface
charge on cell uptake of auxin. Nat. New Biol.
1973;244(139):285-288.
71. Sachs T. Auxins role as an example of the mechanisms of
shoot/root relations. Plant Soil 2005;268:13-19.
72. Sahoo D. Farming the ocean: seaweeds cultivation and
utilization. Aravali, New Delhi, 2000
73. Schaarschmidt S, Roitsch T, Hause B. Arbuscular
mycorrhiza induces gene expression oft he apoplastic
invertase LIN6 in tomato (Lycopersicon esculentum)
roots. J. Exp. Bot. 2006;57:4015-4023.
74. Schobert C, Komor E. The differential transport of
amino acids into the phloem of Ricinus communis L.
Morphological and physiological changes during adventitious root
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
seedlings as shown by the analysis of sieve-tube sap.
Planta 1989;177:342–349.
Spethmann W, Hamzah A. Growth hormone induced
root system types in cuttings of some broad leaved tree
species. Acta Hortic. 1988;226:601–605.
Spinelli F, Fiori G, Noferini M, Sprocatti M, Costa G. A
novel type of seaweed extract as a natural alternative to
the use of iron chelates in strawberry production. Sci.
Hortic. 2010;125:263-269.
Sridhar S, Rengasamy R. Significance of seaweed liquid
fertilizers for minimizing chemical fertilizers and
improving yield of Arachys hypogaea under field trials.
Rec. Res. Sci. Tech. 2010;2:73-80.
Stenzel I, Hause B, Maucher H, Pitzschke A, Miersch O,
Ziegler J, Ryan C, Wasternack C. Allene oxide cyclase
dependence of the wound response and vascular
bundle-specific generation of jasmonates in tomato –
amplification in wound signaling. Plant J. 2003;33:577–
589.
Štefančič M, Štampar F, Veberič R, Osterc G. The levels
of IAA, IAAsp and some phenolics in cherry rootstock
‘GiSelA 5’ leafy cuttings pretreated with IAA and IBA.
Sci. Hortic. 2007;112:399–405.
Taiz L, Zeiger E. Plant physiology (5th ed.). Sunderland,
MA: Sinauer Associates, 2010
Takahashi F, Sato-Nara K, Kobayashi K, Suzuki M, Suzuki
H. Sugar-induced adventitious roots in Arabidopsis
seedlings. J. Plant Res. 2003;116:83– 91.
Tatematsu K, Kumagai S, Muto H, Sato A, Watahiki MK,
Harper RM, Liscum E, Yamamoto KT. MASSUGU2
encodes Aux/IAA19, an auxin-regulated protein that
functions together with the transcriptional activator
NPH4/ ARF7 to regulate differential growth responses of
hypocotyl and formation of lateral roots in Arabidopsis
thaliana. Plant Cell 2004;16(2):379-393.
Thirumaran G, Arumugam M, Arumugam R,
Anantharaman P. Effect of seaweed liquid fertilizer
on growth and pigment concentration of Cyamopsis
tetrogonolaba (L) Taub. Am.-Eur. J. Agr. 2009;2:50-56.
Trobec M, Štampar F, Veberič R, Osterc G. Fluctuations
of different endogenous phenolic compounds and
cinnamic acid in the first days of the rooting process of
cherry rootstock ‘Gisela 5’ leafy cuttings. J. Plant Physiol.
2005;162:589-597.
Trueman, SJ, Richardson DM. Propagation and
chlorophyll fluorescence of Camptotheca acuminata
cuttings. J. Med. Plants Res. 2011;5:1-6.
Urbanek Krajnc A, Ivanuš A., Kristl J. Šušek A. Seaweed
extract elicits the metabolic responses in leaves and
enhances growth of Pelargonium cuttings. Eur. J. Hortic.
Sci. 2012;77:170-181.
Urquhart AA, Joy KW. Transport, metabolism, and
redistribution of xylem-borne amino acids developing
pea shoots. Plant Physiol. 1982;69:1226–1232.
Van Der Kriken WM, Breteler H, Visser MHM.
Uptake and metabolism of indolebutyric acid during
root formation on Malus microcuttings. Acta Bot.
Neerlandica 1992;41:435-442.
Van Staden J, Upfold SJ, Drewes FE. Effect of seaweed
concentrate on growth and development of the marigold
Tagetes patula. J. Appl. Phycol. 1994;6:427-428.
90. Volpert R, Osswald W, Elstner EF. Effects of cinnamic
acid derivates on indole acetic acid oxidation by
peroxidase. Phytochem. 1995;38:19–22.
91. Wasternack C, Hause B. Jasmonates and octadecanoids
– signals in plant stress response and development. In:
Moldave K (eds). Progress in nucleic acid research and
molecular biology. Academic Press, New York, NY,
USA, 2002;165-221.
92. Went FW, Thimann KV. Phytohormones. New York,
The Macmillan Company, 1937
93. Werner T, Holst K, Pors Y, Guivarc’h A, Mustroph
A, Chriqui D, Grimm B, Schmuelling T. Cytokinin
deficiency causes distinct changes of sink and source
parameters in tobacco shoots and roots. J. Exp. Bot.
2008;59:2659-2672.
94. Whapham CA, Blunden G, Jenkins T, Hankins SD.
Significance of betaines in the increased chlorophyll
content of plants treated with seaweed extract. J. Appl.
Phycol. 1993;5:231-234.
95. Woodward AW, Bartel B. Auxin: regulation, action, and
interaction. Ann. Bot. 2005;95(5):707-735.
96. Xu M, Zhu L, Shou H, Wu. A PIN1 family gene,
OsPIN1, involved in auxin-dependent adventitious
root emergence and tillering in rice. Plant Cell Physiol.
2005;46(10):1674-1681.
97. Zimmerman PW, Wilcoxon F. Several chemical growth
substances which cause initiation of roots and other
responses in plants. Contrib. Boyce Thompson Inst.
1935;7:209-229.
Received: July 17, 2012
Accepted in final form: November 6, 2013
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